Using Entity Type Manager to get a list of fields

Get all entity reference fields that target media entities

To get a list of all entity reference fields that target media entities you can use the Entity type manager and the loadByProperties() method.

$fields = \Drupal::entityTypeManager()->getStorage('field_storage_config')->loadByProperties([
  'type' => 'entity_reference',
  'settings' => [
    'target_type' => 'media',
  ],
]);

Get all dynamic entity reference fields

In the same way, you can get a list of dynamic entity reference fields.

$fields = \Drupal::entityTypeManager()->getStorage('field_storage_config')->loadByProperties([
  'type' => 'dynamic_entity_reference',
]);

The $fields variable will contain an array of FieldStorageConfig instances for each field that satisfies the condition.

This won't return fields that are defined as BaseFieldDefinition in your code.